Support finding content by integration in search

[toph-allen]

Support passing an integration to the function implementing the content search endpoint.

client <- connect()

integration <- get_integrations(client)[[1]]
list_of_content_for_integration <- content_search(client, integration = integration)

There's a possibility we'd also want to implement a get_content_for_integration() function as a shorthand (possible because integration objects have a copy of the client).

client <- connect()

content_for_integration <- get_integrations(client)[[1]] |>
  get_content_for_integration()

• Follow-on to Support content search query #272 (implementing content search)
• Supersedes Add function to get content associated with an integration #433 and feat: get content that uses a specified integration #441 (previous issue and PR for a get_content_for_integration()-style function)
• Requires https://github.com/posit-dev/connect/issues/33181 (supporting integrations in content search)